Bleaching of soaps and soapstocks



y 1956 F. 0. JAMES EIAL 2,755,294

BLEACHING OF SOAPS AND SOAPSTOCKS Filed Nov. 6. 1952 F ll? MM WVHW'ORS I W (a w wgxiwishxs WA United States Patent 2,755,294 BLEACHING OF SOAPS AND SOAPSTOCKS Frederick Oliver James, Hoylake, England, and Anthony Humphreys, Douglas, Isle of Man, assig'nors to Lever Brothers Company, New York, N. Y., a corporation of Maine Application November 6, 1952, Serial No. 319,954

Claims priority, application Great Britain November 9, 1951 22 Claims. (31. 260-419 The present invention relates to the bleaching of .soaps and soapstocks. For convenience, the term soap is used hereinafter to include soap and soapstocks wherever the context so permits.

The bleaching of soaps is usually carried out by mixing a bleaching agent with molten soap contained in at soap pan at or near the boiling point with or without the addition of water. Sodium hypochlorite is the bleaching agent most frequently used, but other bleaching agents have also been employed.

It has been found that an appreciable improvement over this method of bleaching can be obtained if the bleaching agent is continuously fed into a stream of molten soap in either an open or closed system and then rapidly and intimately mixed with the soap.

Accordingly, the present invention provides a process for bleaching soaps consisting in continuously feeding a hypochlorite bleaching agent into a stream of molten soap and ensuring rapid and intimate mixing of the bleaching agent with the soap. p

The phrase feeding a hypochlorite bleaching agent into a stream of molten soap whenever mentioned in the specification or in the claims is intended to cover the addition of a hypochlorite bleaching agent in any suitable form, suchas a solution. The term hypochlorite bleaching agent also includes substances such as chlorine which will form a hypochlorite in situ when a caustic alkali is present. Sodium hypochlorite, however, is the preferred bleaching agent. 7

It has' also been found that the bleaching of soap according to the present invention may in many cases be further improved by the addition of one or several substances acting as bleaching aids for the process. These bleaching aids are thought to act as accelerators and/or promoters in the process.

Examples of bleaching aids for use with hypochlorites in this process are: persalts, such as sodium persulphate or sodium percarbonate, peroxides, such as hydrogen peroxide, 'or oxygen; The use of bleaching aids is of particular advantage in the bleaching of highly coloured soaps, such as red palm oil or green tallow soaps. In some cases, however, such as in the bleaching of relatively good quality tallow soaps, the use of bleaching aids may not lead to better results.

Hydrogen peroxide is the bleaching aid most conveniently used in conjunction with a hypochlorite bleaching agent as it is available in a relatively stable form at all concentrations and as it leaves no residue other than water, when its function has been performed.

The hypochlorite bleaching agent is preferably used in amounts of 0.5 to 3% by Weight of the fatty matter, and the amount of bleaching aid used may vary from 0.01 to 0.20% by weight of the fatty matter, the latter percentage being expressed as hydrogen peroxide.

Preferably the bleaching aid is added as soon as inti- -ma'te' mixing of the soap and the hypochlorite bleaching agent is completed. It is advisable to provide, further agitation immediately after the additionofthe bleaching 2,755,294 Patented July 17, 1956 aid. This preferred process may conveniently be carried out by providing continuous agitation from the addition of the hypochlorite bleaching agent at leastuntil the bleaching aid has been intimately mixed with the stream. The bleaching aid may, however, first be intimately mixed with the soap and the hypochlorite bleaching agent then added to the mixture, preferably immediatelyafterwards. It is again advisable to provide further agitation immediately after the addition of the hypochlorite bleaching agent. Care must always be taken that'the hypochlorite bleaching agent and the bleaching aid do not come into contact before either one or the other has been well mixed with the soap. Thus, if agitation is sufficiently vigorous, the hypochlorite bleaching agent and the bleaching aid may be added almost simultaneously.

Rapid mixing is required to ensure that no local conce'ntrations of hypochlorite bleaching agent or bleaching aid occur, since such local concentrations might lead to waste of reagents and, possibly, other undesirable effects, such as uneven bleaching of the soap. The mixing may conveniently be carried out by means of a mechanical stirrer, the blades of which are situated close to the point of introducing the components. Other methods of rapid and intimate mixing may, however, be employed.

Better results are sometimes obtained if the process according to the present invention is carried out under pressure, usually not exceeding about 5atmospheres, particularly if no bleaching aid is used I A suitable apparatus for carrying out the process according to the present invention consists of a tubular vessel containing a stirrer with the blades close to the outlet of pipes feeding in the stream of soap and the bleaching agent respectively. An additional stirrer or stirrers may also be provided at other levels of the vessel if, for example, the bleaching aid is introduced at a different level from that of the soap and hypochlorite bleaching agent and agitation at that level is not sufiiciently vigorous.

It is convenient to use a vertical tubular vessel and to feed in the soap and the hypochlorite bleaching agent near the bottom. The removal of the bleached molten soap may be effected by an overflow over the edge of the vessel, or through an outlet at some other convenient level. The level of soap inside the tubular vessel should be preferably be sufficient to preventaeration in the tube. For instance, a head of cm. has been found convenient for a tubular vessel of 10' cm. diameter. As the bleached soap may be removed continuously, the process according to the present invention can be readily incorporated in a continuous soap manufacturing plant.

It is preferred to' use a measuring or proportioning device, so that the quantities of bleaching agent and molten soap (and water if required or bleaching aid if used) can be accurately measured or controlled, thereby avoiding waste or over-bleaching. The device may be electronic.

The temperature of the mixture at the time of bleaching should preferably be inthe range of 75 C. This may be achieved by bringing the soap to the required temperature before bleaching. A certain amount of temperature control in the reaction zone, whether heating or cooling, may be effected by means such as a jacket or coils through which a heating or cooling medium can be passed. At temperatures below 70 C., mixing ditficulties may be encountered, while at temperatures substantially above 85 C., the bleaching action may become difiicult to control. Good bleaches may in some cases be obtained at temperatures up to C., or even above by operating under pressure. These higher temperatures may conveniently be attained with the use of steam.

When dealing with soapstocks it may be advantageous to saponify and bleach inone operation (by effecting the bleaching in the presence of an alkaline substance) as bleaching of the free oil does not take place until it is saponified. But saponification is more rapid at 100 C. than at the preferred bleaching temperature range of 75-85 C. and it has been established that good bleaches of highly coloured soapstocks such as palm oil soapstock may also be obtained at a temperature of 100 C.

The process according to the present invention may be used for the bleaching of soaps of any fatty matter content and whether grained or ungrained. Before bleaching the soap, it is desirable to wash it with brine or a solution of caustic soda in the normal manner to remove the impurities which normally pass into the washings and which, if not removed, would needlessly consume bleaching agent.

It has been observed that the pH of the mixture tends to be reduced during the bleaching process. The process according to the invention should be carried out under alkaline conditions, a degree of alkalinity corresponding to that of soap being preferred. It has been found that it is usually necessary to add alkali to the soap to be bleached in amounts sufficient to ensure that the pH of the mixture does not fall below the desired value as the reaction proceeds.

When dealing with soap solutions containing an appreciable amount of neutral oil, such as, for instance, soapstocks produced in the refining of oils, it is particularly desirable to wash the soap soltuions after the neutral oil contained therein has been saponified but prior to bleaching in order to remove some of the impurities.

The bleaching agent may considerably darken rosin soaps if present in the soap mixture. It is, therefore, advisable to add rosin soaps after the bleaching is completed.

The process according to the present invention represents a considerable improvement over the existing methods for bleaching soaps. Bleaching is carried out under better controlled conditions and at relatively low temperature. The quantity of bleaching agent required in order to obtain the same degree of bleaching is substantially reduced. The electrolyte content can be controlled to suit the nature of the soap and to produce a bleached soap in a suitable condition for passing into a continuous washing system. The process according to the present invention is of particular advantage when applied to the bleaching of soaps made from highly coloured oils, such as red palm oil and green tallow soaps, which cannot be bleached satisfactorily by existing methods.

The invention will now be illustrated by means of the following diagrammatic drawings in which:

Fig. l is a sectional elevation of an apparatus for carrying out the process of the invention.

Fig. 2 is a plan view of Fig. 1 through line AA'.

Referring to the drawings, water, bleaching agent, bleaching aid and molten soap are fed at the bottom of a tubular vessel 8 through pipes l, 2, 3 and 4 respectively. The liquids are agitated by means of an agitator 10 consisting of three blades as shown in Fig. 2 operated by a motor 11 through a shaft 12. The vessel may be heated or cooled by a jacket 9 through which hot or cold substances are circulated via pipes 5 and 6. The outlet for the bleached soap 7 is provided in the upper part of the vessel 8. At the outlet 7 some device may be provided which will allow pressure to build up inside the apparatus. Further pipes may also be provided at convenient levels for the introduction of steam, if required, or other desired substances.

The following examples of the bleaching of soap illustrate the present invention without limiting it. Use was made in the examples of an apparatus similar to that just described.

Example 1 A soap was made from a fat charge consisting of 55% red palm oil, 35% palm kernel oil and 10% groundnut oil, washed to a glycerine content of less than 1% and settled from a grain to 62% fatty matter (F. M.) content.

Soap, sodium hypochlorite and water were fed into the bleaching tube continuously at the points indicated on the diagram. Rates of flow, temperatures and concentrations are tabulated below:

Material lbs. per Iemp.,

hour C.

Soap input at 62% F. M. content 1, 262 82 Sodium hypochlorito solution containing 14.7%

Soap output 1, 522 70 1 Equivalent to 1.88 NaOCl expressed as percentage of fatty matter The bleached soap when it was boiled up was in the closed condition. It was adjusted for alkali content, treated with 0.1% sodium hydrosulphite expressed as a percentage of fatty matter, grained out and fitted in the customary manner. The colour of the soap was a pale orange.

Example 2 A soap was made from a fat charge consisting of 55% red palm oil, 35% palm kernel oil and 10% groundnut acid oil, washed to a glycerine content of less than 1% and settled from a grain to 62% F. M. content. The settled soap, sodium hypochlorite, hydrogen peroxide, and water were fed into the bleaching tube continuously at the points indicated on the diagram at the following controlled rates,

1 Equivalent to 1.88 NaOCl expressed as percentage of fatty matter. 2 Equivalent to 0.10 H102 expressed as percentage of fatty matter.

The bleached soap on boiling up was in the closed condition and was adjusted for alkali content and treated with 0.1% sodium hydrosulphite expressed as percentage of fatty matter. It was then grained out and fitted in the customary manner. The fitted soap was pale cream in colour.

Example 3 A soap was made from a fat charge consisting of red palm oil and 25% palm kernel oil, washed to a glycerine content of less than 1% and settled from a grain to 57% F. M. content. The settled soap, sodium hypochlorite, hydrogen peroxide and water were fed into the bleaching tube continuously at the points indicated on the diagram at the following controlled rates, temperatures and concentrations:

Material lbs. per Temp,

hour C.

Soap input at 57% F. M. content 1,250 93 Sodium hypochlorite solution containing 14.0%

NaOCl 1 100 20 Hydrogen peroxide solution containing 3.5% H20: 27 20 Water 130 15 Soap output 1, 507

1 Equivalent to 1.96 NaOCl expressed as percentage of fatty matter. I Equivalent to 0.13 H201 expressed as percentage of fatty matter.

The soap leaving the tube was in the open condition and was heated by means of steam to a temperature of C. and the lye separated. The resulting curd at a F. M. content of 54% was fitted in the normal manner. The fitted soap was pale yellowish cream in colour.

Example A groundnut oil soapsto 'clc containing 18.7% {of fatty acids as soap and 6.6% of neutral oil was fed into the bleaching tube continuouslyftogether with sodium hypochlorite and caustic soda solution suificient to saponify the fat in the soapstock at the following controlled rates and temperatures 1 Equivalent to 1.32 NaOOl expressed as percentage of fatty matter.

Material lbs. per Temp,

. hour 0.

Soapstock input containing 24.9% F. as soap.. 1, 400 84 Sodium hypochlorite solution containing 14.2%

moor s5 20 Soapstock output 1, 435 82 1 Equivalent to 1.42 NaOCI expressed as percentage of fatty matter.

The bleached soapstock was grained'outand fitted in the customary manner. The settled soap was greyish cream in colour.

Example 6 A deep orange coloured palm oil soapstock containing 20% of fatty acids as soap and 13% of neutral oil was boiled in a soap pan with caustic soda to complete the saponification of the neutral oil. The product was fed continuously into the bleaching tube with sodium hypochlorite, hydrogen peroxide and water at the following controlled rates and temperatures:

Material lbs. per Temp,

hour O.

Soapstock input containing 31% F. M. as $02.11.. 1, 350 88 Sodium hypochlorite containing 13.9% I IaOCl 63 15 Hydrogen peroxide solution containing 2.5%

H202 2 15 15 Water 72 15 Soapstock output 1,500 82 1 Equivalent to 1.50 NaOCl expressed as percentage of fatty matter. 2 Equivalent to 0.09 H102 expressed as percentage of fatty matter.

The bleached soapstock was grained out and fitted in the customary manner. The settled soap was yellowish cream in colour.

Example 7 A deep orange coloured palm oil soapstock containing 21.5% of fatty acids as soap and 4.8% of neutral oil was fed continuously into the bleaching tube with sodium hypochlorite, hydrogen peroxide, caustic soda solution,

'waterand steam at the following controlled rates and temperatures: i

Material lbs. per Temp,

hour C.

Soapstock input containing 21.5% fatty acids as soap and 4.8% neu ral oil. 1,170 90 Sodium hypochlorite solution containing 12.6%

NaOQl 50 20 Hydrogen peroxide solution 0 taining 3.1% H20: 10 20 Caustic Soda solution conta' mg 22% Na'z0. 70 Water 140 80 Steam to raise temperature of mixture to 100 Soapstock output- 1, 440

1 Equivalent to 2.05 ,Na00l expressed as percentageoi fatty matter. 2 Equivalent to 0.10 1120; expressed as percentage of fatty matter.

The bleached and saponified soapstock was boiled, grained outahd'fitted in the customary manner. The

-- settled soap was yellowish cream in colour.

Example 8 A soap was made from a fat charge consisting of 80% red palm oil and 20% coconut oil, washed to a glycerine (content of less than 1% and settled from a grain to 54% F. M. content. Soap sodium hypochlorite, sodium percarbonate solution and water were fed continuously into the bleaching tube at the following controlled rates and temperatures The bleached soap after graining out and fitting and settling in the customary manner was pale cream in colour.

We claim:

1. A method of bleaching soap comprising continuously feeding a hypochlorite bleaching agent into a stream of molten soap and ensuring rapid and intimate mixing of the bleaching agent with the soap.

2. A process according to claim 1 which is carried out under pressure.

3. A process according to claim 1 which is carried out at a temperature from about 75 to about C.

4. A method of bleaching soap comprising continuously feeding a hypochlorite bleaching agent into a stream of molten soap and ensuring rapid and intimate mixing of the bleaching agent with the soap, continuously feeding a bleaching aid selected from the group consisting of peroxides, persalts and oxygen into the intimate mixture of the soap and the hypochlorite bleaching agent and ensuring rapid and intimate mixing of the bleaching aid with the mixture.

5. A process according to claim 4 which is carried out at a temperature from about 75 to about 85 C.

6. A method of bleaching soap comprising continuously feeding a bleaching aid selected from the group consisting of peroxides, persalts and oxygen into a stream of molten soap, ensuring rapid and intimate mixing of the bleaching aid with the soap, and then continuously feeding a hypochlorite bleaching agent into the mixture of the soap and the bleaching aid and ensuring rapid and intimate mixing of the hypochlorite bleaching agent with the mixture of the bleaching aid and the soap.

7. A process according to claim 6 which is carried out at a temperature from about 75 to about 85 C.

8. A method of bleaching soap comprising continuously feeding a hypochlorite bleaching agent into a stream of molten soap at one end of an elongated zoneand ensuring rapid and intimate mixing, continuously feeding a bleaching aid selected from the group consisting of peroxides, persalts and oxygen into the mixture of the hypochlorite bleaching agent and the soap and ensuring rapid and intimate mixing of the bleaching aid with the mixture of the hypochlorite bleaching agent and the soap, continuously passing the resultant mixture through the said zone at an elevated temperature and continuously discharging the bleached soap at the opposite end of the zone.

9. A process according to claim 8 in which the elevated temperature is from about 75 to about 85 C.

10. A process according to claim 8 in which the soap to be bleached comprises red palm oil soap.

11. A process according to claim 8 in which the soap to be bleached comprises green tallow soap.

12. A method of bleaching soap comprising continuously feeding a bleaching aid selected from the group con sisting of peroxides, persalts and oxygen into a stream of molten soap and ensuring rapid and intimate mixing of the bleaching aid with the soap, continuously feeding a hypochlorite bleaching agent into the mixture of the soap and the bleaching aid and ensuring rapid and intimate mixing of the hypochlorite bleaching agent with the mixture of the soap and the bleaching aid, continuously passing the resultant mixture through an elongated zone at an elevated temperature and continuously discharging the bleached soap at the opposite end of the zone.

13. A process according to claim 12 in which the elevated temperature is from about 75 to about 85 C.

14. A process according to claim 12 inwhich the soap to be bleached comprises red palm oil soap.

15. A process according to claim 12 in which the soap to be bleached comprises green tallow soap.

16. A method of bleaching soap comprising continuously and separately feeding soap, water, sodium hypochlorite and hydrogen peroxide into one end of an elongated zone and ensuring rapid and intimate mixing, continuously passing the mixture through the said zone at a temperature in the range of about 75 to about 85 C. and continuously discharging the bleached soap at the opposite end of the zone.

17. A process according to claim 16 in which the soap to bebIeached comprises red palm oil soap.

18. A process according to claim 16 in which the soap to be bleached comprises green tallow soap.

1-9. A method of bleaching soap comprising continuously and separately feeding soap, water and sodium hypochlorite into one end of an elongated zone and ensuring rapid and intimate mixing, continuously feeding hydrogen peroxide into the said zone and ensuring rapid and intimate mixing of the hydrogen peroxide with the mixture of soap, water and sodium hypochlorite, passing the resultant mixture through the elongated zone at a temperature in the range of about 75 to about 85 C. and at a rate to accomplish the requisite bleaching during the residence of the soap in the zone and continuously discharging the bleached soap at the opposite end of the zone.

20. A process according to claim 19 in which the soap to be bleached comprises red palm oil soap.

21. A process according to claim 19 in which the soap to be bleached comprises green tallow soap.

22. A method of bleaching soap comprising continuously feeding 0.5 to 3.0% of a hypochlorite bleaching agent into a stream of molten soap and ensuring rapid and intimate mixing of the bleaching agent with the soap, and continuously feeding 0.01 to 0.20%, expressed as hydrogen peroxide, of a bleaching aid selected from the group consisting of peroxides, persalts and oxygen into the intimate mixture of the soap and the hypochlorite bleaching agent and ensuring rapid and intimate mixture of the bleaching aid with the mixture, the percentages of bleaching agent and bleaching aid being based on the weight of fatty matter in the soap.

References Cited in the file of this patent UNITED STATES PATENTS 2,057,959 Kling Oct. 20, 1936 2,433,662 Hampel Dec. 30, 1947 2,592,226 Woodward Apr. 8, 1952 OTHER REFERENCES Bailey: Industrial Oil and Fat Products, 2nd edition (1951), page 853. 

1. A METHOD OF BLEACHING SOAP COMPRISING CONTINUOUSLY FEEDING A HYPOCHLORITE BLEACHING AGENT INTO A STREAM OF MOLTEN SOAP AND ENSURING RAPID AND INTIMATE MIXING OF THE BLEACHING AGENT WITH THE SOAP. 